Experimental Study On Cyclic Behavior Of Wenzhou Reconstituted Soft Clay Under Different Stress Hostories

With the continuous expansion of southeast coastal cities,reclamation technology is widely used.In view of the short consolidation time of the hydraulic fill soil layer formed by this technology,the consolidation degree of the soft soil foundation in this area is low,and it is under-consolidated.Usually,it is necessary to carry out overload preloading method to treat the soft soil foundation in this area.Therefore,under-consolidated soil and over-consolidated soil with different stress history exist in the reclamation area of southeast coast.At present,a large number of municipal and transportation infrastructure construction are being carried out in these areas,such as Ningbo Taizhou Wenzhou double track expressway,Wenzhou City railway and other sections.These soft soil foundations are not only subjected to static load such as self-weight,but also bear complex cyclic load such as traffic load for a long time,which is easy to produce excessive deformation and lead to frequent engineering accidents.In this paper,dynamic cyclic consolidation test and hollow cylinder torsional shear test are used to study the cyclic behavior of Wenzhou reconstituted soft clay under different stress histories.The specific contents include:1.Under-consolidated reconstituted soft clay samples with different degrees of consolidation are obtained by realizing the degree of stress relaxation.Confined cyclic consolidation tests with different degrees of consolidation and different cyclic stress ratios were carried out under drained conditions.The results show that:(1)The axial strain decreases with the increase of consolidation degree and increases with the increase of cyclic stress ratio.(2)Based on the "rapid growth","critical" and "stable" characteristics of the deformation development of underconsolidated soil with the increase of cyclic stress ratio,the critical cyclic stress ratio suitable for different degrees of consolidation is determined.(3)The cumulative strain prediction formula considering the influence of cyclic stress ratio,degree of consolidation and cycle number is established.2.By controlling the dissipation degree of excess pore water pressure,under-consolidated reconstituted soft soil samples with different degrees of consolidation are obtained.A series of pure principal stress axis rotation undrained tests with constant medium principal stress coefficient are carried out under different generalized deviatoric stress levels.Four basic strain components,elastic modulus and non-coaxial development law are studied.The experimental results show that:(1)The strain component decreases with the increase of the degree of consolidation,and increases with the increase of the generalized deviator stress;(2)The elastic modulus decreases with the increase of the number of cycles,and has different development under different degrees of consolidation and different generalized deviator stress;(3)It is found that the non-coaxial angle becomes obvious with the increase of the degree of consolidation and the decrease of the generalized deviator stress.However,the direction angle of large principal stress corresponding to each peak value of non-coaxial angle does not change with the increase of cycle number.3.By controlling the pre-consolidation pressure and vertical pressure,the over-consolidation reconstituted soft clay samples with different overconsolidation ratios are obtained.Confined cyclic consolidation tests with different over-consolidation ratios and different cyclic cycles were carried out under drained conditions.The experimental results show that(1)The axial strain always decreases with the increase of over-consolidation ratio.When the over-consolidation ratio exceeds 4,the increase rate of axial strain decreases significantly.(2)When the cycle period increases from 10 s to 40 s,the axial strain first increases and then decreases.(3)According to the summary and improvement of the cumulative strain prediction model,the cumulative strain prediction formula of over-consolidated soil considering cyclic period is obtained.